Circuit interrupter



Oct. 19, 1954 w, LEEDS 2,692,320

CIRCUIT INTERRUPTEIR Filed Aug. 5, 1950 3 Sheets-Sheet l Fig.l.

Fig.2. 5- 20a Q9 4 r1 WITNESSES: 52 iNVENTOR fi Winthrop M. Leed s. I 6 BY 3/ ATTORNEZ Oct. 19, 1954 Filed Aug. 5, 1950 w. M. LEEDS 2,692,320

CIRCUIT INTERRUPTER 3 Sheets-Sheet 2 WITNESSES: INVENTOR fiz /A Winfhrop M. Leeds.

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3 Sheets-Sheet 3 Filed Aug. 5, 1950 Fig.5.

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UNITED STATES PATENT OFFICE CIRCUIT INTERRUPTER Winthrop M. Leeds, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa a corporation of Pennsylvania Application August 5, 1950, Serial No. 177,918

14 Claims. 1

This invention relates to circuit interrupters in general, and more particularly to mounting arrangements and piston structures for circuit interrupters.

A general object of my invention is to provide an improved simplified type of circuit interrupter in which the interrupting structure is effective, simple, rugged, being able to withstand shock without deteriorating effects, and with improved means for opening the contact structure and for expediting low current interruption. 7

Another object is to provide an improved mounting arrangement for a circuit interrupter adapted to be placed within a tank or other enclosure.

A more specific object is to provide an improved liquid break circuit interrupter mounted in an improved manner and hydraulically operated. Preferably, the hydraulic operation is in part utilized to facilitate low current interruption,

particularly charging currents which result when the interrupter opens a circuit connected to capacitor banks, or (fie-energizes a transmission line.

Another object is to provide an improved liquid break circuit interrupter in which improved structural mounting arrangements are employed to utilize the available space to the fullest extent.

Further objects and advantages will readily become apparent upon reading the following specification taken in conjunction with the drawings in which:

Figure 1- is a vertical sectional view taken through a liquid break typeof circuit interrupter embodying my invention, the contact structure being shown in the partially open circuit position, the left-hand interrupting assembly being shown in vertical section and the right-hand interrupting assembly being shown in side elevation;

Fig. 2 is a fragmentary vertical sectional view of a modified type of interrupting assembly in which liquid flow to the interrupting unit is delayed for a predetermined time;

Fig. 3 is a side elevational view, partly in vertical section, of a modified type of liquid break circuit interrupter, the left-hand arc extinguishing unit being shown in vertical section, the righthand extinguish-ing unit being shown in side elevation, and the contact structure being shown in the partially open circuit position;

Fig. 4 is a plan view of the interrupterof Fig. 3 takenalong the line IV--IV thereof Fig. 5 is aside elevational view of another modified type of liquid break circuit interrupter embodying myinvention, the contact structure have arisen with respect to bending stresses,

shock under both opening and closing operations, and maintenance of alignment between the suspended contact assemblies and the rapidly operated moving contact cross-arm on the end of the lift rod. The speed of movement of the lower contacts in the contact assemblies is limited to the speed of the cross-arm unless complicated multiplying lever systems are added. Where separate delayed-action pistons are used in each contact assembly for the interruption of charging current, there is the possibility of inaccurate synchronizing of the oil pistons, increasing the probability of arc restrikin-g and resultant switching surges. My invention is designed to obviate these difficulties.

Referring to Fig. 1, it will be noted that in my improved interrupter; there is provided a grounded metallic tank or enclosure I filled to the level 2 with asuitable arc extinguishing liquid 3, in this instance, circuit breaker oil.

Passing through the upper cover 4 of the tank I are a pair of terminal bushings indicated by the reference characters 5, 6 to the lower ends of which are secured stationary disconnect contacts I, 8. Cooperating with the stationary disconnect contacts I, 8 are a pair of movable disconnect contact blades 9, H), pivotally supported at H to the upper ends of a pair of identical interrupting assemblies, generally indicated by the reference character l2.

The interrupting assemblies I2 are supported and hydraulically interconnected by a hollow support M, the latter resting upon an insulating pedestal l3, preferably formed of a suitable ceramic material able to withstand shock and having the desired mechanical strength.

Within each interrupting assembly 12 is a relatively' stationary contact it, a movable intermediate contact I! provided with a perforated flange I8 and biased downwardly by a compression spring is. There is also provided in each interrupting assembly I Z a lower movable interrupting contact 20 secured to a hydraulic piston 2I and biased upwardly in a circuit closing direction by a compression spring 22. The piston 2I moves within a metallic operating cylinder 23 which passes through the hollow support I4 and is secured thereto.

A perforated cap 24 closes the lower end of the operating cylinder 23, and a flexible shunt 25 electrically interconnects the lower movable interrupting contact 20 to the cap 24 and hence through the cylinder 23 to its interconnecting metallic hollow member I4.

From the foregoing, it will be apparent that in the closed circuit position of the interrupter, not shown, the electrical circuit therethrough extends through the left-hand terminal bushing to stationary disconnect contact I, then through movable disconnect blade 9 to the top metallic cover plate 25 of the left-hand interrupting assembly I2. The circuit then extends through the stationary contact I6, intermediate contacts I! to the lower movable interrupting contact 20. The circuit then extends by way of flexible conductor 25 to lower cap 24 and then through the metallic operating cylinder 23 to hollow conducting support I4. The electrical circuit then extends through the right-hand interrupting assemblage I2 in a similar manner to the righthand terminal bushing 6.

A portion of the hollow support I4 extends upwardly, as at 21, to form a piston cylinder within which is reciprocally movable operating piston 28 having a plurality of one-way acting valves 29 provided therein. Connected to the operating piston 28 is a piston rod 30, the upper extension of which constitutes a lift rod, generally designated by the reference character 3|. A pair of stops 32, 33 are rigidly secured to the lift rod 3i to engage an actuating collar 34 surrounding the lift rod 3| and having a pair of bifurcated links 35 pivotally mounted thereon, as at 35. The free legs 31 of the bifurcated links 35 are pivotally connected, as at 38, to crank arms 39, two of which are provided for each interrupting assembly I2. The two crank arms 39 are rigidly secured to the outer ends of shafts II, intermediate the ends of which are rigidly secured the movable disconnect blades 9, I0. Y Thus, downward opening motion of the lift rod 3|, not only causes motion of the operat ng piston 23 within the operating cylinder 21, but also, after a predetermined time, causes engagement between the stop 32 and the collar 34 to effect thereby rotation of the crank arms 39 and hence opening rotative motion of the movable disconnect blades 9, ID to the dotted line positions thereof as indicated.

It will be apparent that downward motion of the piston 28 causes liquid, in this instance oil, to flow in the direction indicated by the arrows to cause downward opening motion of the pistons 21, and hence the lower movable interrupting contacts 28. At first, this causes formation of a pressure-generating arc 40, established between the contacts I8, II, the intermediate contact I'I remaining in abutting engagement with the upper tip of the interrupting contact 20, by virtue of the biasing action exerted by the compression spring i9. After the flange I8 has struck the plate 4I, however, continued downward motion of the interrupting contact 20 establishes an interrupting are 42 between the intermediate and interrupting contacts I1, 20.

The pressure-generating are 40 generates pressure within the oil which completely fills the interrupting assembly I2. This pressure, generated by the pressure-generating are 48, causes oil to flow downwardly as indicated by the arrows and inwardly toward the interrupting are 42 through pairs of inlet passages 43. After contacting the interrupting arc 42, the oil passes through orifices 44 and exhausts out of the interrupting assembly I2 through pairs of exhaust passages 45. 1

Reference may be had to United States Patent 2,467,760, issued April 19, 1948, to Leon R. Ludwig, Benjamin P. Baker and Winthrop M. Leeds and assigned to the assignee of the instant application for particulars of the passage structure provided within the interrupting assembly I2; it merely being necessary to know for an understanding of my invention that the pressure-generating chamber 46 adjacent the pressure-generating are 40 is substantially closed, and the interrupting passage 47, along which the interrupting are 42 is drawn, is vented to the region exteriorly of the interrupting assembly I2 by the pairs of exhaust passages 45.

During the interruption of relatively high currents, the pressure generated within the pressuregenerating chamber 46 by the pressure-generating are 40 is sufficient to cause the requisite quantity of oil to flow under a suitable pressure head to effectively extinguish the interrupting are 42. During such high pressure conditions, the valve 48, spring-biased to a closed position, remains closed, thereby preventing any oil passing from the hollow member I4 into the interrupting assembly I2 to assist in effecting the extinction of the interrupting are 42 therein.

As soon as the are is extinguished, the pressure within the interrupting assembly I2 falls quickly, valve 48 opens and oil flows in under pressure from the piston 28 until the end of the stroke is reached. This oil flow serves to flush out residual gas, carbon and metallic particles from the interrupting chamber. 7

However, during the interruption of relatively low amperage currents, such as magnetizing currents, or charging currents, the pressure generated within the pressure-generating chamber 46 by the pressure-generating are 40 may be inadequate to cause the requisite quantity of oil to flow toward the interrupting are 42. In this event, the pressure of the oil caused by downward opening motion of the piston 28 may be greater than the pressure within the interrupting assembly I2, so that the valve 48 will then be opened by the difference in pressure, to thereby permit the entrance of oil from the operating cylinder 23 through the valve 48 and into the interrupting assembly I2 to effect the extinction of the interrupting arc 42 therein.

Thus, the piston 28 is not only efiective to hydraulically bring about downward opening motion of the rod-shaped interrupting contacts 20, but also assists, during low current interruption, to cause entrance of oil past the valve means 48 and into the interrupting passage 41 to effect extinction of the interrupting are 42 therein.

At the end of the opening operation, following extinction of the arcs 40, 42 and hence interrupting of the circuit passing through the interrupter, the stop 32 strikes the collar 34 to effect opening of the disconnect contacts 9 and I0. When the disconnect contacts 9,' I0 have been opened, the piston 28, at this time, is immediately adjacent the hollow member I4 and ceases its opening motion. Oil leakage past the pistons H and 28 permit upward closing motion of the contact rods to take place. The contact springs 22 will effect reclosure of the contact structure, the oil above the pistons 2| being forced through the valves 48 and out the exhaust passages 45. The compression springs 22 are made sufficiently strong to cause the interrupting contacts 20 to pick up the intermediate contacts l1 and cause reclosure between the stationary and intermediate contacts it, 11. The contact structure is then closed within the interrupting assemblies (2, the disconnect gaps between the contacts 1, 9 and 8, in being relied upon to maintain the circuit open.

The closing operation of the interrupter will now be described. To close the interrupter, the lift rod 31 is moved upwardly by suitable mechanism, which forms no part of my invention. The upward closing movement of the lift rod 3! causes engagement between the stop 33 and the collar 34, thereby effecting through the bifurcated links 35' and the crank-arms 39 ciosing motion of the movable disconnect blades 9, lil. When the movable disconnect blades 9, It have struck the stationary disconnect contacts 1, 8, the circuit is completed through the interrupter. During the upward closing motion of the piston 28, the valves 29 open to permit unidirectional flow of oil from the region Ali past the valves 29 and into the region 5i! within the operating cylinder 2?.

The interrupter is then in, a condition ready to open the circuit if such action is desired.

Fig. 2 shows, in fragmentary fashion, a modified arrangement to delay the entrance of oil from. the region 5d into the interrupting assembly 5!. As before, the interrupting contact 2% is secured to a piston 2Ia which moves within an operating cylinder 23!], being biased upwardly therein by a compression spring 22a. It is impossible for oil from the region 50 to enter the interrupting assembly 5! until after the piston 2m has uncovered the inlet opening 52 to permit the oil to pass upwardly and into the interrupting assembly 5! as indicated by the arrows. Thus, a predetermined time is provided before the entrance of oil from the region 5% into the interrupting assembly 5!. This particular time delay before entrance of the oil into the interrupting assembly 5! may be very important, as brought out in United States patent application, filed February 5, 1948, Serial No. 6,436, now United States Patent 2,592,635, issued April 15, 1952, to Winthrop M. Leeds, Robert E. Friedrich and Francis J. Fry, and assigned to the assignee of the instant patent. This application shows that for the effective interruption of charging currents, it is necessary to delay the application of the oil flow until a predetermined time has elapsed following contact parting. By providing the time-delay structure of Fig. 2, it is possible to accurately time the entrance of oil from the region Shinto the interrupting assembly 5|.

Figs. 3 and 4 illustrate a further embodiment of my invention. It will be observed that a pair of axially aligned interrupting assemblies 53 are provided, being supported upon a pedestal l3. The movable disconnect blades 9a, Ella are pivotally mounted, as at 54, to the end plates 55 of the interrupting assemblies 53. The stationary contacts Ifia are provided adjacent the other ends of the interrupting assemblies 53, being secured to the end plates 55, the latter being fixedly secured to the operating cylinder 21a.

With this arrangement, the vertical height of the interrupter may be considerably decreased so that the interrupter may be more readily adapted for certain types of installations. The operation is fundamentally the same as heretofore described in connection with Fig. 1, that is, downward opening motion of the lift rod 3l'effecting working travel of the piston 28, and hence a forcing of oil past the valve means 51 to effect opening of the interrupting contacts 29 by the passage of oil through the inlet opening 58.

It will be observed that with this embodiment of my invention, the pressure within the region 50 is always greater initially than the pressure within the interrupting assemblies 53, inasmuch as no pressure exists within the interrupting assemblies 53 until arcing takes place. Since initially the contact structure is closed, and no arcing consequently takes place when a fault current is first established through the contacts, the pressure caused by downward opening motion of the piston 28 is always effective to open the valves 5'6 and hence effect opening of the contact structure. The pressure-generating and interrupting arcs at, 32 are established as heretofore described. During high current interruption, the pressure generated within the interrupting assembly 53 may be sufiicient to cause closure of the valves 5?, but this is unimportant since the contact structure will continue to open under the effect of the generated pressure. During low current interruption, as in the arrangement illustrated in Fig. 1, the liquid flow caused by downward motion of the piston 23 may assist in interruption of the interrupting arc 42. As before, engagement of the stop 32 with the collar 3 is effective to cause through the links 59 opening rotative motion of the movable disconnect blades 9a, ma to the dotted line positions shown in Fig. 3.

At the end of the opening operation, contact spring 22 will effect reclosure of the contact structure, the oil to the right of piston 2| being forced through opening 58 and out of the exhaust passages d5. Hence, the contact structure is reclosed within the units 53 in the fully open circuit position thereof, and reliance is had, as heretofore, upon the disconnect gaps between the disconnect contacts "to, Ed and 3a, Ilia to hold th voltage.

To effect reclosing of the circuit through the interrupter, it is merely necessary to cause upward closing motion of the lift rod 3!, which effects abutting engagement between the stop 33 and the slidable collar 34 to effect thereby reclosure of the disconnect contacts Ea, 9a and 8a, Ilia to effect reclosure of the circuit interrupter.

Figs. 5 and 6 show a further embodiment of the invention, somewhat similar to that of Figs. 3 and 4 in that the interrupting assemblies are disposed horizontally, but lateral width is here conserved. In other words, referring to Fig. 6, it will be observed that the interrupting assemblies 6t and their piston cylinders 65 are overlapped to conserve lateral space. The disconnect lades 9b, lilb are pivotally mounted, as at 32, to the end plates 83 of the interrupting assembly 60. The piston 28 moves within an operating cylinder 2??) which is bored out of a casting 64. lhe operating cylinders 5! are secured in any suitable manner, as by welding to the casting 64. It is obvious, referring to Fig. 6, that the stationary contact end of the interrupting assemblies 69 is adjacent the end plate 63, and the movable interrupting contact end of the interrupting assembly 6!! is at the opposite end of the interrupting assembly 6% adjacent the operating cylinders 6|. In other words, the contact structure of the -Fig. 3.

interrupting assembly so is reversed with respect to the sectional view or the contact structure shown of the interrupting assembly 53 of The hydraulic connection between the operating cylinder 21b and the piston cylinders 6| may be similar to that set forth in Fig. 1. Figs. and 6, consequently, merely show a horizontal construction of the interrupting assemblies 60 positioned in overlapping relationship to conserve lateral space, and yet providing an interrupter having small vertical height. As before, the pedestal l3 supports the weight of the interrupting assemblies.

From the foregoing, it will be apparent that my invention is adaptable to any circuit interrupter, particularly those of the liquid-break type, and is specifically intended for application to high speed, high voltage, outdoor oil circuit breakers. The interrupting assemblies are mounted on an insulating pedestal support 13 at the center of the surrounding steel tank forming each pole of the oil circuit breaker. I have provided high speed arcing contacts, hydraulically driven by a centrally located oil piston operated by the usual accelerating springs and operating mechanism. The centrally applied downward force results only in balanced compressive forces in the supporting column. Electrical connection to the terminal bushings is made and broken by separate isolator or disconnect switch blades 9, I0. Retrieving springs reclose the arcing contacts immediately following a circuit interruption and opening of the isolators. These springs 22 also provide contact pressure for carrying the load current when the isolators are closed.

Since there is a relatively large capacitance to the tank from the piston and supporting assembly, voltage dividing resistors R are desirable to equalize the recovery voltage across each interrupting assembly. At the end of the opening stroke, the oil pressure falls and the springs 22 reclose the arcing contacts.

It will be apparent that the closing operation is very simple since the breaker mechanism immediately raises the drive rod 3 i, the piston valves 29 allowing oil to flow into the cylinder 2'! as the piston 28 is raised. The bumper 33 on the drive rod closes the circuit with the isolator contacts 9 and In. It is to be noted that high speed reclosing is possible without the isolators. In other words, for ultra-high speed reclosing, where the lift rod 31 is reversed at an intermediate point in its opening operation before the stop 32 strikes the collar 34 to effect thereby opening of the isolators 9, 10, the contact structure will merely be opened and may be reclosed following such reversal of the lift rod 3!. As a result, the interrupter is particularly adaptable for such ultrahigh speed reclosing operations without any modification of the lift rod construction 3| utilizing the two stops 32, 33. It will also be noted that only a single piston 28 is utilized in the disclosed construction, the single piston supplementing the fluid flow in both interrupting assemblies to assist in low current interruption.

Although I have shown and described specific structures, it is clearly to be understood that the same were merely for the purpose of illustrating the invention, and that changes and modifica-, tions may readily be made therein by those skilled in the art without departing from the spirit and scope of the appended claims.

I claim as my invention:

1. A circuit interrupter including an enclosure,

a pair of serially connected interrupting assemblies disposed within the enclosure, means for supporting the two interrupting assemblies within the enclosure, a pair of terminal bushings extending into the enclosure and having stationary disconnect contacts depending therefrom at the interior ends thereof, a pair of movable isolating blades supported upon the two interrupting assemblies and movable into and out of engagement with the stationary disconnect contacts, contact structure disposed in each interrupting assembly, and means for sequentially causing the opening first of the contact structures and then of the disconnect contacts.

2. A circuit interrupter including an enclosure, a pair of serially connected interrupting assemblies disposed within the enclosure, means for supporting the two interrupting assemblies within the enclosure, a pair of terminal bushings extending into the enclosure and having disconnect contacts depending therefrom, a pair of disconnect contacts associated with the interrupting assemblies, contact structure disposed in each interrupting assembly, and means for sequentially causing the opening first of the contact structures and then of the disconnect contacts.

3. A circuit interrupter of the liquid break type including a grounded tank at least partly filled with liquid and having a pair of serially connected interrupting assemblies disposed therewithin, an insulating pedestal disposed at the bottom of the tank for supporting the two interrupting assemblies, a pair of terminal bushings extending through the top of the tank and having disconnect contacts secured to their interior ends, a pair of cooperating disconnect contacts associated with the interrupting assemblies, contact structure disposed in each interrupting assembly, and means for sequentially causing the opening first of the contact structures and then of the disconnect contacts.

4. A circuit interrupter of the liquid break type including a grounded tank at least partly filled with liquid and having a pair of serially connected interrupting assemblies disposed therewithin, an insulating pedestal disposed at the bottom of the tank for supporting the two interrupting assemblies, a pair of terminal bushings extending through the top of the tank and having stationary disconnect contacts secured to their interior ends, a pair of cooperating movable disconnect contacts associated with the interrupting assemblies, contact structure disposed in each interrupting assembly, and means for sequentially causing the opening first of the contact structures and then of the disconnect contacts.

5. A circuit interrupter of the liquid break type including a grounded tank at least partly filled with liquid and having a pair of serially connected interrupting assemblies disposed therewithin, an insulating pedestal disposed at the bottom of the tank for supporting the two interrupting assemblies, a pair of terminal bushings extending through the top of the tank and having disconnect contacts secured to their interior ends, a pair of cooperating disconnect contacts associated with the interrupting assemblies, hydraulically operated contact structure disposed in each interrupting assembly, spring means for biasing the contact structures to the closed position, and piston means for causing the opening of the contact structures.

6. A circuit interrupter of the liquid break type 9 including a grounded tank at least partly filled with liquid and having a pair of serially connected interrupting assemblies disposed therewithin, an insulating pedestal disposed at the bottom of the tank for supporting the two interrupting assemblies, a pair of terminal bushings extending through the top of the tank and having stationary disconnect contacts secured to their interior ends, a pair of movable disconnect contacts associated with the interrupting assemblies, hydraulically operated contact structure disposed within each unit, actuating means including piston structure operable to open the contact structures hydraulically, means biasing both contact struc-' tures to the closed circuit position, said actuating means also including means for opening the disconnect contacts at a predetermined time in the opening operation following are extinction.

7. A circuit interrupter of the liquid break type including a grounded tank at least partially filled with liquid and having a pair of serially connected interrupting assemblies disposed therewithin, an insulating pedestal disposed at the bottom of the tank for supporting the two interrupting assemblies, a pair of terminal bushings extending through the top of the tank and having stationary disconnect contacts secured to their interior ends, a pair of movable disconnect contacts associated with the interrupting assemblies, hydraulically operated contact structure disposed within each unit, actuating means including piston structure operable to open the contact structures hydraulically, means biasing both contact structures to the closed circuit position, said actuating means also including means for opening the disconnect contacts at a predetermined time in the opening operation following are extinction, and the interrupting assemblies being disposed substantially horizontally within the tank.

8. A circuit interrupter of the liquid break type including a grounded tank at least partly filled with liquid and having a pair of serially connected interrupting assemblies disposed therewithin, an insulating pedestal disposed at the bottom of the tank for supporting the two interrupting assemblies, a pair of terminal bushings extending through the top of the tank and having stationary disconnect contacts secured to their interior ends, a pair of movable disconnect contacts associated with the interrupting assemblies, hydraulically operated contact structure disposed within each unit, actuating means including piston structure operable to open the contact structures hydraulically, means biasing both contact structures to the closed circuit position, said actuating means also including means for opening the disconnect contacts at a predetermined time in the opening operation following arc extinction, and the interrupting assemblies being disposed substantially horizontally within the tank in at least partially overlapped relationship.

9. A circuit interrupter of the liquid break type including a grounded tank at least partly filled with liquid and having a pair of serially connected interrupting assemblies disposed therewithin, an insulating pedestal disposed at the bottom of the tank for supporting the two interrupting assemblies, a pair of terminal bushings extending through the top of the tank and having stationary disconnect contacts secured to their interior ends, a pair of movable disconnect contacts associated with the interrupting assemblies, a hydraulic operating piston situated between the interrupting assemblies and disposed in substantial alignment with the insulating pedestal, a piston rod for moving the hydraulic piston, and means movable with the piston rod for opening and closing the movable disconnect contacts. 7

it). A circuit interrupter of the liquid break type including a grounded tank at least partly filled with liquid and having a pair of serially connected interrupting assemblies disposed therewithin, an insulating pedestal disposed at the bottom of the tank for supporting the two interrupting assemblies, a pair of terminal bushings extending through the top of the tank and having stationary disconnect contacts secured to their interior ends, a pair of movable disconnect contacts associated with the interrupting assemblies, hydraulically operated contact structure disposed within each unit, actuating means including piston structure operable to open the contact structures hydraulically, means biasing both contact structures to the closed circuit position, said piston structure including a piston situated between the interrupting assemblies and disposed in substantial alignment with the insulating pedestal, said actuating means also including means for opening the disconnect contacts at a predetermined time in the opening operation following are extinction.

11. A circuit interrupter including an enclosure, at least one interrupting assembly disposed interiorly within the enclosure, at least one terminal bushing extending interiorly within the enclosure, means other than said termnial bushing for supporting said interrupting assembly within said enclosure, a stationary disconnecting contact associated with the interior end of said terminal bushing, a movable disconnecting blade associated with said interrupting assembly and cooperable with the stationary disconnecting contact to form an isolating gap in the circuit, contact structure associated with said interrupting assembly for establishing an arc, and means for sequentially causing establishment of the arc and subsequently movement of the movable disconnecting blade to form the isolating gap.

12. A circuit interrupter of the liquid break type including a grounded tank filled with liquid, at least one interrupting assembly disposed interiorly within the tank and submerged in the liquid therein, at least one terminal bushing extending interiorly within the grounded tank, means other than said terminal bushing for supporting said interrupting assembly within said grounded tank, a stationary disconnecting contact associated with the interior end of said terminal bushing, a movable disconnecting blade associated with said interrupting assembly and cooperable with the stationary disconnecting contact to form an isolating gap in the circuit, contact structure associated with said interrupting assembly for establishing an arc, and means for sequentially causing establishment of the arc and subsequently movement of the movable disconnecting blade to form the isolating gap.

13. A circuit interrupter including contact means for establishing an arc, said contact means including a movable contact, an operating cylinder, an operating piston secured to said movable contact and movable within the operating cylinder, an inlet opening in the side wall of the operating cylinder leading from the operating cylinder on the non-working Side of the operating piston when the latter is in the closed circuit position to the region adjacent arc establishment, and means for forcing fluid under pressure into the operating cylinder to move the movable operating piston past the inlet opening and so expose the inlet opening to provide a delayed fluid flow toward the arc.

14. A circuit interrupter of the liquid break type including a grounded tank filled with liquid, a pair of serially connected interrupting assemblies disposed within the grounded tank and submerged in the liquid disposed therein, means for supporting the two interrupting assemblies within the tank, a pair of terminal bushings extending into the tank and having stationary disconnecting contacts depending therefrom at the interior ends thereof, a pair of movable isolating blades supported upon the two interrupting assemblies and movable into and out of engagement with the stationary disconnecting contacts, contact structure disposed within each interrupt- 12 ing assembly, and hydraulic means for sequentially causing the opening first of the contact structure and then of the disconnecting contacts including an operating rod movable substantially centrally of the tank between the pair of terminal bushings.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,029,366 Hewlett June 11, 1912 1,133,032 Jacobs Mar. 23, 1915 1,532,081 Rankin Mar. 31, 1925 2,219,171 Balachowsky Oct. 22, 1940 2,250,216 Biermanns July 22, 1941 2,310,905 Blandford Feb. 9, 1943 2,392,201 Thumim et a1. Jan. 1, 1946 2,430,128 Lerstrup Nov. 4, 1947 2,477,788 Cumming Aug. 2, 1949 

